<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    * {
        margin: 0;
        padding: 0;
        box-sizing: border-box;
    }

    ul {

        list-style: none;
    }

    .mi {
        position: relative;
        width: 223px;
        margin: 100px auto;
    }

    .mi input {
        width: 223px;
        height: 48px;
        padding: 0 10px;
        font-size: 14px;
        line-height: 48px;
        border: 1px solid #e0e0e0;
        outline: none;
    }

    .mi .search {
        border: 1px solid #ff6700;
    }

    .result-list {
        display: none;
        position: absolute;
        left: 0;
        top: 48px;
        width: 223px;
        border: 1px solid #ff6700;
        border-top: 0;
        background: #fff;
    }

    .result-list a {
        display: block;
        padding: 6px 15px;
        font-size: 12px;
        color: #424242;
        text-decoration: none;
    }

    .result-list a:hover {
        background-color: #eee;
    }
</style>
</head>
<body>
  <div class="mi">
    <input type="search" placeholder="小米笔记本">
    <ul class="result-list">
        <li><a href="#">全部商品</a></li>
        <li><a href="#">小米11</a></li>
        <li><a href="#">小米10S</a></li>
        <li><a href="#">小米笔记本</a></li>
        <li><a href="#">小米手机</a></li>
        <li><a href="#">黑鲨4</a></li>
        <li><a href="#">空调</a></li>
    </ul>
  </div>

  <script>
    //1获取元素
    const input = document.querySelector('[type=search]')
    const ul = document.querySelector('.result-list')
    //2监听事件 获得焦点
    input.addEventListener('focus',function () {
      // ul显示
      ul.style.display = 'block'
      // 添加一个带有颜色边框的类名
      input.classList.add('search')
    })
    //3监听事件，失去焦点
    input.addEventListener('blur',function () {
      ul.style.display = 'none'
      input.classList.remove('search')//移除这个有颜色边框的类名
    })
  </script>
</body>
</html>